linux-kernel - Re: [PATCH] x86-64: disable the GART before allocate aperture

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Date:	Fri, 22 Jun 2007 15:41:24 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andi Kleen <ak@...e.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Muli Ben-Yehuda <muli@...ibm.com>,
	Yinghai Lu <Yinghai.Lu@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86-64: disable the GART before allocate aperture

Andi Kleen <ak@...e.de> writes:

> On Friday 22 June 2007 22:33, Alan Cox wrote:
>> You've got mapped live gart pages from the previous kernel. Even if you
>> disable the gart before a memset 
>
> It's probably too late then. It could also interfere with other operations.
> If anything the GART should be disabled during kexec shutdown. Perhaps we just 
> need a suitable suspend function that does that. Eric, any preferences? 

Well it would be a shutdown method not a suspend method.  The authors of
the suspend code thought sharing code with the reboot and the rmmod case
didn't make sense.

For a normal kexec into another kernel I think this makes sense.

>> you may well have the video card using 
>> gart translations and possibly live IOMMU mappings for devices using it
>> via bus mastering - and those will cause you MCE exceptions with a
>> corrupt cpu context flag (ie not nicely recoverable).
>
> We disable those machine checks on K8 because they're not fully reliable.

For the kexec on panic not shutting the hardware down if at all possible is
the ideal.  There I think we need a mode to not touch a chunk of the iommu
and reserve it for the kexec on panic kernel (or perhaps just use the
swiotlb code if we need bounce buffers at all).

Eric
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